The present invention relates to a device which measures a voltage of each of plural voltage supplies coupled in series and collects the measurement results, and, in particular, the present invention can be utilized suitably for a semiconductor device which configures the device.
Currently, an electric vehicle which employs a motor as a driving source for traveling of the vehicle is developed by not only automakers but other companies or groups. In order to drive a motor, an in-vehicle power supply which produces a high voltage of several hundred volts is required. This power source is realized by a battery system comprised of a series coupling of many unit cells (battery cells) each of which produces a voltage of several volts. Such a battery system needs to measure the voltage of each of plural unit cells coupled in series with high accuracy, in order to determine the state of the battery (for example, an overcharge state, an overdischarge state, the remaining amount of charge) under all environments including at the time of traveling and electric charging of a vehicle. A battery system may incur serious risks, such as ignition and explosion, at the time of occurrence of abnormal conditions; therefore, in order to operate the battery system safely, a fail-safe solution is adopted in the voltage measurement device.
A battery control system is usually comprised of a supervisory IC (Integrated Circuit), a fault monitor IC (secondary protection IC), an MCU (Micro Controller Unit), and others. The supervisory IC monitors the state of a battery cell and outputs state data (mainly battery voltage). The supervisory IC is provided with an analog-to-digital converter circuit (ADC), measures the battery voltage of a unit cell to an accuracy of about 5 mV, and outputs the measurement result in response to an instruction from the MCU. The fault monitor IC monitors the voltage of a battery cell and outputs an abnormality detection signal when the monitored voltage deviates from a predetermined voltage range. In the case of a lithium-ion battery, for example, the fault monitor IC outputs an abnormality detection signal, noting that it is an overdischarge state when the unit cell voltage becomes less than 2V, and outputs an abnormality detection signal, noting that it is an overcharge state when the unit cell voltage becomes greater than 4.5V. The MCU controls the supervisory IC and the secondary protection IC, and at the same time, controls the entire battery control system on the basis of the outputs of the supervisory IC and the fault monitor IC. The MCU summarizes the state data outputted from the supervisory IC in real time, and performs suitable control on the basis of the state data.
In particular, severe functional safety standards are applied to a vehicle electronic control system. In order to fulfill these severe standards, many kinds of diagnosis function are provided in the battery control system. The examples include the detection function of disconnection between a node of unit cells of an assembled battery and a terminal of the supervisory IC, and self-diagnosis function of each blocks, such as ADC, etc. The fault monitor IC which can detect an overcharge state and an overdischarge state is frequently employed for realizing such functional safety.
On the other hand, the reduction in cost is also strongly demanded for the battery control system. For that purpose, it is assumed to be better to integrate the supervisory IC and the fault monitor IC on a single semiconductor chip. When the fault monitor IC is employed for realization of the functional safety, it is desirable to perform the integration with the function maintained.
Patent Literature 1 discloses the technique of adding to a supervisory IC the function capable of detecting disconnection between a node of unit cells in an assembled battery and a terminal of the supervisory IC. The disconnection is detected by observing a voltage drop which occurs at the time when the node and the ground is selectively short-circuited with a resistor and a switch. The measurement of the voltage drop is performed by utilizing an ADC provided in the supervisory IC for measurement of the cell voltage as the original function.
Patent Literature 2 realizes the function of detecting disconnection between a node of unit cells in an assembled battery and a terminal of a supervisory IC, by employing an overvoltage detection comparator and a low-voltage detection comparator. In the normal operation without disconnection, the overvoltage detection comparator determines that an abnormality is detected when a cell voltage becomes greater than a predetermined value, and the low-voltage detection comparator determines that an abnormality is detected when a cell voltage becomes less than a predetermined value. Patent Literature 2 points out that “when disconnection occurs in the voltage measurement wiring, it is important to detect the disconnection immediately and to take fail-safe action” (Paragragh 0004).
Patent Literature 3 discloses an invention which has improved the invention disclosed by Patent Literature 2. Patent Literature 3 solves an issue that an output of a voltage sensor module is accidentally outputted due to disconnection of wiring, thereby causing an unstable output as a battery voltage monitoring device.
Patent Literature 4 discloses a battery voltage monitoring device which can check whether a comparator for monitoring the occurrence of an overcharge state or an overdischarge state is working properly, in the state where the voltage of each battery cell configuring an assembled battery is in the normal voltage range.